Coefficients of Quality of Road Materials.
| Granitic gravel | 23 | ·8 | ||||
| Quartz gravel | 21 | ·4 | ||||
| Trap | 20 | ·0 | ||||
| Quartz | 10 | ·0 | to | 25 | ·0 | (in one instance 4·8) |
| Basalt | 12 | ·0 | „ | 20 | ·0 | |
| Porphyry | 10 | ·0 | „ | 20 | ·0 | (in one instance 5·0) |
| Quartzite | 11 | ·0 | „ | 18 | ·0 | |
| Devonian schist | 16 | ·0 | ||||
| Schist | 4 | ·0 | to | 12 | ·0 | |
| Sandstone | 12 | ·0 | „ | 16 | ·0 | |
| Granite | 6 | ·0 | „ | 20 | ·0 | (generally 10·0 to 12·0) |
| Syenite | 12 | ·0 | ||||
| Gneiss | 9 | ·0 | to | 12 | ·0 | |
| Silicious pebbles and gravel | 8 | ·0 | „ | 19 | ·0 | (in one instance 6·0) |
| Silex | 8 | ·0 | „ | 16 | ·0 | |
| Chalk flints | 7 | ·0 | „ | 11 | ·6 | |
| Silicious limestone | 6 | ·0 | „ | 18 | ·0 | (generally about 10·0 to 12·0) |
| Compact limestone | 14 | ·0 | ||||
| Magnesian limestone | 16 | ·0 | ||||
| Carboniferous limestone | 9 | ·0 | ||||
| Oolitic limestone | 5 | ·0 | to | 12 | ·0 | |
| Lias limestone | 5 | ·0 | „ | 10 | ·0 | |
| Juranic limestone | 5 | ·0 | „ | 8 | ·0 | |
| Limestone | 5 | ·0 | „ | 12 | ·0 | |
| Mean of all France | 10 | ·63 | ||||
It will be seen by the above table how different are the results obtained from materials of the same character.
Breaking stone for the purpose of using it as a road metal was, until comparatively recent years, always effected by hand; now, as in other cases, machinery has stept in and somewhat supplanted manual labour. Hand-broken road metal, however, still finds favour with road surveyors; it is better broken, and in some districts, the occupation finds employment for persons who otherwise would be thrown on the rates for support.
In breaking stone by hand the breaker sits and strikes the stone with a small cast-steel chisel-faced hammer, weighing about one pound, at the end of a long, straight-grained but flexible ash stick.[33] The breaker also has another hammer, weighing about five pounds, with which he reduces the size of the large stones before breaking them into the proper size for road metal. This latter size is often a matter of choice, some engineers preferring it to be broken so small as will pass through a ring of only 1¹⁄₂ inch in diameter; others are content with 3 inches, especially where the roads are steam rolled. An old method of gauging used to be “such a size as the stone breaker could put in his mouth,” but this was unsatisfactory to all persons concerned, and “to pass all ways through a ring of 2¹⁄₂ inches internal diameter” is now the size most generally adopted.
Mr. Codrington says[34] “a good stone breaker will break 2 cubic yards of hard limestone to the ordinary gauge in a day, and some men will break more. Hard silicious stones and igneous rocks can only be broken at the rate of 1¹⁄₂ or of 1 cube yard per day; of some of the toughest, such as Guernsey granite, a man can only break on an average half a cube yard per day. River gravel, field stones, or flints, which are already of a small size, can be broken at the rate of 3 or 4 cube yards per day.”
This may be taken as fairly representing a day’s work, the price for breaking however must vary considerably in different localities on account of the variety of the stones to be broken and the value of labour; in some districts the road metal does not cost more than 1s. per cube yard, in others 2s. 6d. and 2s. 8d. is not considered too high, and it was to meet and reduce this great expense that steam stone-breaking machines have been introduced. These machines are known as “Ellison’s,” “Newall and Archer’s,” “Hope’s,” and “Blake’s,” the latter being that which is best known and most generally used in this country.
“ARCHER’S” STONE BREAKER.
